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// Microsoft Developer & Platform Evangelism
// 
// Copyright (c) Microsoft Corporation. All rights reserved.
// 
// THIS CODE AND INFORMATION ARE PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND, 
// EITHER EXPRESSED OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE IMPLIED WARRANTIES 
// OF MERCHANTABILITY AND/OR FITNESS FOR A PARTICULAR PURPOSE.
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// herein are fictitious.  No association with any real company,
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//Copyright 2010 Microsoft Corporation
//
//Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. 
//You may obtain a copy of the License at 
//
//http://www.apache.org/licenses/LICENSE-2.0 
//
//Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an 
//"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 
//See the License for the specific language governing permissions and limitations under the License.


namespace System.Data.Services.Http
{
    using System;
    using System.Collections.Generic;

    internal class CaseInsensitiveAscii : IEqualityComparer<string>, IComparer<string>
    {
        internal static readonly byte[] AsciiToLower = new byte[]
        {
            0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 
            0x10, 0x11, 0x12, 0x13, 20, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 30, 0x1f, 
            0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27, 40, 0x29, 0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f, 
            0x30, 0x31, 50, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x3a, 0x3b, 60, 0x3d, 0x3e, 0x3f, 
            0x40, 0x61, 0x62, 0x63, 100, 0x65, 0x66, 0x67, 0x68, 0x69, 0x6a, 0x6b, 0x6c, 0x6d, 110, 0x6f, 
            0x70, 0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77, 120, 0x79, 0x7a, 0x5b, 0x5c, 0x5d, 0x5e, 0x5f, 
            0x60, 0x61, 0x62, 0x63, 100, 0x65, 0x66, 0x67, 0x68, 0x69, 0x6a, 0x6b, 0x6c, 0x6d, 110, 0x6f, 
            0x70, 0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77, 120, 0x79, 0x7a, 0x7b, 0x7c, 0x7d, 0x7e, 0x7f, 
            0x80, 0x81, 130, 0x83, 0x84, 0x85, 0x86, 0x87, 0x88, 0x89, 0x8a, 0x8b, 140, 0x8d, 0x8e, 0x8f, 
            0x90, 0x91, 0x92, 0x93, 0x94, 0x95, 150, 0x97, 0x98, 0x99, 0x9a, 0x9b, 0x9c, 0x9d, 0x9e, 0x9f, 
            160, 0xa1, 0xa2, 0xa3, 0xa4, 0xa5, 0xa6, 0xa7, 0xa8, 0xa9, 170, 0xab, 0xac, 0xad, 0xae, 0xaf, 
            0xb0, 0xb1, 0xb2, 0xb3, 180, 0xb5, 0xb6, 0xb7, 0xb8, 0xb9, 0xba, 0xbb, 0xbc, 0xbd, 190, 0xbf, 
            0xc0, 0xc1, 0xc2, 0xc3, 0xc4, 0xc5, 0xc6, 0xc7, 200, 0xc9, 0xca, 0xcb, 0xcc, 0xcd, 0xce, 0xcf, 
            0xd0, 0xd1, 210, 0xd3, 0xd4, 0xd5, 0xd6, 0xd7, 0xd8, 0xd9, 0xda, 0xdb, 220, 0xdd, 0xde, 0xdf, 
            0xe0, 0xe1, 0xe2, 0xe3, 0xe4, 0xe5, 230, 0xe7, 0xe8, 0xe9, 0xea, 0xeb, 0xec, 0xed, 0xee, 0xef, 
            240, 0xf1, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7, 0xf8, 0xf9, 250, 0xfb, 0xfc, 0xfd, 0xfe, 0xff
        };

        internal static readonly System.Data.Services.Http.CaseInsensitiveAscii StaticInstance = new System.Data.Services.Http.CaseInsensitiveAscii();

        public int Compare(string firstString, string secondString)
        {
            if (firstString == null)
            {
                return ((secondString == null) ? 0 : -1);
            }

            if (secondString == null)
            {
                return 1;
            }
            
            int result = firstString.Length - secondString.Length;
            int comparisons = (result > 0) ? secondString.Length : firstString.Length;
            for (int index = 0; index < comparisons; index++)
            {
                int difference = AsciiToLower[firstString[index]] - AsciiToLower[secondString[index]];
                if (difference != 0)
                {
                    return difference;
                }
            }
            
            return result;
        }

        public bool Equals(string firstString, string secondString)
        {
            if (firstString == null)
            {
                return (secondString == null);
            }
            
            if (secondString != null)
            {
                int index = firstString.Length;
                if ((index == secondString.Length) && (FastGetHashCode(firstString) == FastGetHashCode(secondString)))
                {
                    int comparisons = firstString.Length;
                    while (index > 0)
                    {
                        index--;
                        if (AsciiToLower[firstString[index]] != AsciiToLower[secondString[index]])
                        {
                            return false;
                        }
                    }

                    return true;
                }
            }
            
            return false;
        }

        public int GetHashCode(string text)
        {
            if (text == null)
            {
                return 0;
            }

            int hashCode = text.Length;
            if (hashCode == 0)
            {
                return 0;
            }
            
            return (hashCode ^ ((AsciiToLower[(byte) text[0]] << 0x18) ^ (AsciiToLower[(byte) text[hashCode - 1]] << 0x10)));
        }

        private static int FastGetHashCode(string text)
        {
            int result = text.Length;
            if (result != 0)
            {
                result ^= (AsciiToLower[(byte)text[0]] << 0x18) ^ (AsciiToLower[(byte)text[result - 1]] << 0x10);
            }
            
            return result;
        }
    }
}
